This project is concerned with mechanisms of DNA packing in vivo, with emphasis on contributions of the intrinsic properties of DNA and its counterion enviroment. The overall goals are to experimentally detail solution conditions leading to spontanteous ordering in concentrated DNA solutions, to unify experimental observations within the framework of theories of semi-rigid polymer and polyelectrolyte behavior, and to describe the DNA packing arrangements and motional dynamics in ordered states. DNA at high concentrations in asqueous solutions of simple electrolyes spontaneously forms ordered, liquid crystalline-like phases and more condensed phases. Ordering is driven principally by the necessity to reduce the volume excluded by DNA, and is expected based on the well characterized behaviors of other semi-rigid, but non-electrolyte polymers. The nature of the ordered phase at a particular concentration and temperature is dependent on the balance of solvent-polymer segment and segment-segment interactions. For polyelectrolytes these interactions are a strong function of ionic strength and counterion valency. Although the condensed forms of DNA obtained by addition of neutral polymers, organic solvents, or polyvalent cations to dilute DNA solutions have been studied extensively, relatively little attention has been paid to ordering phenomena expected and observed at concentrations near those encountered in vivo. Systematic characterization of these phenomena should provide insights into mechanisms of DNA packing in vivo. Initial studies will focus on identifying phases and determining phase diagrams (temperature vs. concentration) for near persistence length (ca. 500A) DNA as a function of monovalent cation strength. These studies will be extended to examine effects of increasing DNA length and substitution of monovalent by multivalent cations (Mg2+, Ca2+, La3+, spermine, spermidine). Full determination of phase diagrams will require several methods including polarized light microscopy, NMR spectroscopy; circular dichroism, birefringence and light scattering measurements; and viscometry. Solid state NMR techniques will also be used to examine effects of ordering on DNA dynamics.